Boston isn't alone. According to the CDC, 41 states have reported widespread influenza activity, and in the last week of 2012, 5.6 percent of doctor's office visits across the country were for influenza-like illnesses. The severity likely stems from this year's predominant virus: H3N2, a strain known to severely affect children and the elderly. Finelli notes that the 2003-2004 flu season, also dominated by H3N2, produced similar numbers. (See "Are You Prepped? The Influenza Roundup.")

In tracking the flu, physicians and public health officials have a host of new surveillance tools at their disposal thanks to crowdsourcing and social media. Such tools let them get a sense of the flu's reach in real time rather than wait weeks for doctor's offices and state health departments to report in.

Pulling data from online sources "is no different than getting information on over-the-counter medication or thermometer purchases [to track against an outbreak]," said Philip Polgreen, an epidemiologist at the University of Iowa.

The most successful of these endeavors, Google Flu Trends, analyzes flu-related Internet search terms like "flu symptoms" or "flu medication" to estimate flu activity in different areas. It tracks flu outbreaks globally.

Another tool, HealthMap, which is sponsored by Boston Children's Hospital, mines online news reports to track outbreaks in real time. Sickweather draws from posts on Twitter and Facebook that mention the flu for its data.

People can be flu-hunters themselves with Flu Near You, a project that asks people to report their symptoms once a week. So far more than 38,000 people have signed up for this crowdsourced virus tracker. And of course, there's an app for that.

Both Finelli, a Flu Near You user, and Polgreen find the new tools exciting but agree that they have limits. "It's not as if we can replace traditional surveillance. It's really just a supplement, but it's timely," said Polgreen.

When people have timely warning that there's flu in the community, they can get vaccinated, and hospitals can plan ahead. According to a 2012 study in Clinical Infectious Diseases, Google Flu Trends has shown promise predicting emergency room flu traffic. Some researchers are even using a combination of the web database and weather data to predict when outbreaks will peak.

As for the current flu season, it's still impossible to predict week-to-week peaks and troughs. "We expect that it will last a few more weeks, but we can never tell how bad it's going to get," said Finelli.

Hospitals are already taking precautionary measures. One Pennsylvania hospital erected a separate emergency room tent for additional flu patients. This week, several Illinois hospitals went on "bypass," alerting local first responders that they're at capacity—due to an uptick in both flu and non-flu cases—so that patients will be taken to alternative facilities, if possible.

In the meantime, the CDC advises vaccination, first and foremost. On the bright side, the flu vaccine being used this year is a good match for the H3N2 strain. Though Finelli cautions, "Sometimes drifted strains pop up toward the end of the season."

It looks like there won't be shortages of seasonal flu vaccine like there have been in past years. HealthMap sports a Flu Vaccine Finder to make it a snap to find a dose nearby. And if the flu-shot line at the neighborhood pharmacy seems overwhelming, more health departments and clinics are offering drive-through options.